Aircraft components including items such as wing skins and other covers are increasingly being made from composite materials, for example laminates. It is known to fasten the leading and trailing edge covers of a wing to the wing skin using butt-straps located along the joint between the leading and trailing edge covers and the wing skin. These butt-straps secure the covers in place and ensure that the leading and trailing edges of the covers are properly aligned with the corresponding trailing and leading edges of the wing skin.
Conventionally, a metallic butt-strap 1 is used as shown in cross-section in FIG. 1 and described in WO 2007/071905. The butt-strap is attached to the inner mould line (IML) face of the wing skin that generally faces towards the interior of the wing. Prior art butt-strap 1 has a stepped, z-shaped profile, with a short vertical portion 1a joining two horizontal plate portions 1b, c. In this example, plate 1b fits over a portion of the IML face of the aircraft's wing skin 2 such that the leading edge of skin 2 butts up against vertical portion 1a. This is bolted in place with bolt 3 that is countersunk into skin 2 on its outer-mould-line (OML) face.
Plate 1c is attached to the structure that is to be fixed to the leading edge of the cover. For example a D-nose leading edge skin 4 is shown attached to a wing cover leading edge 5 (FIG. 2). In order to reduce erosion of the composite skin 2 by airflow 6, the D-nose skin 4 is usually chosen to be sufficiently thick to overhang the leading edge 5 of skin 2. However, it is found that aerodynamic erosion still occurs and the increased thickness also increases drag. Aerodynamic erosion is often exacerbated when composite materials are used.
The prior-art butt-strap is also vulnerable to bird strike and similar collisions. FIG. 3 shows schematically how an impact on the leading-edge structure (not shown) attached by butt-strap 1 can lead to catastrophic forces on bolt 3. The present invention seeks to ameliorate at least some of the abovementioned problems.